Category Archives: Eastern and Central Pacific

TCs between Mexico and Hawaii

Hurricane Vance Prompts a Tropical Storm Watch for Parts of Mexico

Although the upper level wind shear is increasing over Hurricane Vance it has maintained its intensity today.  At 10:00 p.m. EST on Monday the center of Hurricane Vance was located at latitude 17.4°N and longitude 110.6°W which put it about 485 miles southwest of Mazatlan, Mexico.  Vance was moving toward the north-northeast at 13 m.p.h.  The maximum sustained wind speed was 110 m.p.h. and the minimum surface pressure was 965 mb.  A Tropical Storm Watch has been issued for the portion of the coast from Mazatan to Topolobampo, Mexico.

An upper level trough approaching southern California is generating southwesterly winds that are starting to affect Hurricane Vance.  The outflow is being inhibited on the western side of the hurricane and the upper level cirrus clouds show indications of being pushed toward the northeast.  It is possible that the circulation around Vance is beginning to tilt toward the northeast with height.  In addition, it looks like some drier air may be wrapping around the southwestern side of the circulation.  Increased wind shear and drier air should start weakening Vance and the shear could be strong enough to weaken it quickly at times.

The southwesterly winds in the upper level trough are expected to pull Vance toward the northeast and the center could reach the coast of Mexico in 36-48 hours.  Vance is likely to be much weaker when it gets to the coast but a Tropical Storm Watch has been issued as a precaution.  Moisture associated with the circulation around Vance is likely to enhance the rainfall over parts of Mexico during the middle portion of the week.

 

Tropical Storm Vance Intensifies Into a Hurricane

After an extended period when drier air and wind shear inhibited the organizational processes in Tropical Storm Vance, it has intensified rapidly in recent hours and it is now a hurricane.  At 10:00 a.m. EST on Sunday the center of Hurricane Vance was located at latitude 11.9°N and longitude 107.5°W which put it about 535 miles south-southwest of Manzanillo, Mexico.  Vance was moving toward the northwest at 15 m.p.h.  The maximum sustained wind speed was 80 m.p.h. and the minimum surface pressure was 990 mb.

Vance is moving around the western end of a ridge of high pressure over Mexico.  A large upper level trough west of California will begin to affect Vance as it moves farther north.  The trough is expected to turn Vance toward the northeast early next week.  The track forecast becomes more challenging for the period when Vance could be approaching the coast of Mexico.  Much of the guidance from the numerical models suggests that the upper level winds could be strong enough to separate the upper portion of Vance’s circulation from the lower level rotation.  If that happens, then the middle and upper portions of the circulation could be transported across Mexico, while the surface low gets left behind and meanders southeast of Baja California.

Vance is over water where the Sea Surface Temperature is near 29°C and the upper level winds are relatively light.  So, the period of rapid intensification could continue for another 12-24 hours.  When the upper level trough approaches Vance from the northwest on Monday, the wind shear will increase and Vance will start to weaken and it could weaken quickly.  Even if the low level center of Vance does not make landfall, moisture in the middle and upper portions of the circulation could enhance precipitation over Mexico next week.

Tropical Storm Vance Forms South of Acapulco

More thunderstorms developed near the center of a slow moving area of low pressure south of Mexico and the National Hurricane Center classified the system as Tropical Storm Vance.  At 5:00 p.m. EDT the center of Vance was located at latitude 11.0°N and longitude 101.0°W which put it about 415 miles south of Acapulco, Mexico.  Vance was moving toward the west at 5 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and the minimum surface pressure was 1005 mb.  Vance is the 20th named tropical cyclone for form over the Eastern North Pacific during 2014, which is the most since 1992.

Vance is being steered toward the west by an upper level ridge to its north.  Vance is expected to take a long, clockwise path as it moves around the western edge of the ridge.  Some recent guidance from numerical models suggests that Vance could move farther westward than was indicated in previous model forecasts.   Eventually, when Vance moves farther north, it is anticipated that it will be turned northeastward by a large trough off the west coast of North America.  The trough could pull Vance toward the west coast of Mexico sometime next week.

There are southwesterly winds blowing over the top of Vance in the upper levels and the result is that most of the thunderstorms are developing north and east of the center.  The shear is expected to decrease on Friday.  Vance will be moving over Sea Surface Temperatures (SSTs) that are warmer than 29°C.  So, there will be sufficient energy for intensification and some guidance is indicating that Vance could become a hurricane.   When the upper level trough begins to affect Vance, the wind shear will increase and it could be on a weakening trend when it turns toward the coast of Mexico next week.

Tropical Storm Trudy Forms Southeast of Acapulco

A center of circulation formed within a large area of low pressure south of the coast of Mexico and the system has been classified as Tropical Storm Trudy.  At 11:00 p.m. EDT on Friday the center of Tropical Storm Trudy was located at latitude 15.6°N and longitude 99.0°W which put it about 100 miles southeast  of Acapulco, Mexico.  Trudy was moving toward the north at 8 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and the minimum surface pressure was 1005 mb.  The government of Mexico has issued a Tropical Storm Warning for the portion of the coast from Tecpan de Galeana to Laguna de Chacahua.

A high pressure system over the northern Gulf of Mexico is steering Trudy northward and this motion is expected to continue on Saturday.  Trudy is likely to make landfall on the Mexican coast during the next 24 hours.  The greatest risks are from heavy rainfall and flooding.

Trudy is over warm Sea Surface Temperatures and the upper level winds are not strong.  So, the environment is conducive to intensification.  However, the circulation around Trudy will interact with land soon and there is a limited time during which intensification could occur.

There is a possibility that the middle level circulation of Trudy could cross Mexico and interact with a stationary front over the Bay of Campeche to spin up a low pressure system over the southern Gulf of Mexico next week.

Trudy is the first T-named storm to form over the Eastern North Pacific since Tina in 1992.

Ana Reaches Hurricane Intensity Near Hawaii

The structure and internal organization of Tropical Storm Ana has increased during the past 12 hours and it has intensified into a hurricane.  At 5:00 p.m. EDT the center of Hurricane Ana was located at latitude 16.4°N and longitude 155.2°W which put it about 230 miles south of Hilo and about 380 miles south-southeast of Honolulu, Hawaii.  Ana was moving toward the west-northwest at 14 m.p.h.  The maximum sustained wind speed was 75 m.p.h. and the minimum surface pressure was 987 mb.

The high pressure system that was steering Ana toward the west is weakening as an upper level trough approaches from the northwest.  The result of the interaction of the two systems is to steer Ana more toward the northwest.  Guidance from numerical models suggests that the center of Ana could stay south of the Hawaiian islands.  A new high pressure system is expected to build north of Ana and turn it back onto a more westward track in a couple of days.  The timing of that turn could determine how much of an effect Ana has on Hawaii.  A deviation of the track farther to the north would cause Ana to have a greater impact.  Tropical Storm Watches have been issued for Hawaii County, for Maui County including the islands of Maui, Molokai, Lanai and Kahoolwe, for Oahu, and for Kauai County including the islands of Kauai and Niihau.

The wind shear over Ana has decreased and some further intensification is possible.  When the upper level trough gets closer to Ana, the wind shear will increase and the hurricane should start to weaken.

Simon Intensifies Into a Major Hurricane

Hurricane Simon intensified rapidly on Saturday and it is now a Major Hurricane.  At 5:00 p.m. EDT the center of Hurricane Simon was located at latitude 20.6°N and longitude 115.0°W which put it about 365 miles west-southwest of the southern tip of Baja California and about 495 miles south of Punta Eugenia, Mexico.  Simon was moving toward the west-northwest at 14 m.p.h.  The maximum sustained wind speed was 120 m.p.h. and the minimum surface pressure was 950 mb.

Simon is the 8th hurricane to reach Major Hurricane intensity over the Eastern North Pacific during 2014.  This ties the record for the most Major Hurricanes in one year in that basin, which was set previously in 1983, 1992 and 1993.

Simon is moving around the western edge of a ridge centered over northern Mexico.  It should turn more toward the north on Sunday.  As Simon moves farther north, it will eventually move toward the northeast.  It could approach Baja California by the middle of next week.

Simon may be on the threshold of an eyewall replacement cycle.  If it goes through one of those cycles, there will be some fluctuations in intensity.  When Simon moves west of Baja California it will move over cooler Sea Surface Temperatures and begin to weaken.  Simon is likely to be a weakening tropical cyclone when it nears Baja California.

 

Tropial Storm Simon Intensifying West of Mexico

At 5:00 p.m. EDT on Friday the center of Tropical Storm Simon was located at latitude 18.8°N and longitude 110.6°W which put it about 285 miles south of the southern tip of Baja California.  Simon was moving toward the west-northwest at 9 m.p.h.  The maximum sustained wind speed was 65 m.p.h. and the minimum surface pressure was estimated to be 993 mb.

Simon appears to be developing a tight inner core and there are indications on visible satellite imagery that an eye might be forming.  Upper level winds have lessened and Simon is over warm Sea Surface Temperatures.  So, further intensification is likely and Simon will probably become a hurricane during the weekend.

Simon is being steered to the west-northwest by a mid-level ridge over northern Mexico.  It will likely turn more toward the north as it reaches the western extent of that ridge.  Guidance from the numerical models suggests two possibilities once Simon moves west of Baja California.  Some models are suggesting that it will turn northeastward and make landfall near the central portion of the Baja peninsula.  Another group of models is suggesting that Simon will weaken and stall west of Baja California.  It is too early to be certain which scenario is more likely.

Simon is the 18th named tropical cyclone to form over the Eastern North Pacific during 2014.  This equals the number of named tropical storms that formed over that region in 2013.

 

Tropical Depression 19E Forms West of Mexico

The active hurricane season over the Eastern North Pacific Ocean continues.  An area of thunderstorms west of Mexico developed a surface circulation and a core of convection near the center.  As a result it was classified as Tropical Depression Nineteen-E (TD19E).  At 11:00 p.m. EDT the center of TD19E was located at latitude 17.8°N and longitude 105.4°W which put it about 110 miles southwest of Manzanillo, Mexico and about 455 miles south of the southern tip of Baja California.  TD19E was moving toward the west-northwest at 10 m.p.h.  The maximum sustained wind speed was 35 m.p.h. and the minimum surface pressure was 1003 mb.

The same upper level ridge of high pressure over northern Mexico that has been in place during much of the hurricane season will steer TD19E toward the west-northwest during the next day or two.  As TD19E rounds the western edge of the ridge it will turn more toward the north and it could follow a path similar to the one taken by Hurricane Rachel.

The upper level ridge is producing some northeasterly winds and wind shear over TD19E.  The shear is forecast to weaken and some intensification of TD19E is likely while it remains over warm Sea Surface Temperatures.

 

Rachel Intensifies into a Hurricane

The northeasterly winds in the upper levels that were generating wind shear over Tropical Storm Rachel lessened on Saturday and it intensified into the 12th Eastern North Pacific hurricane of 2014.  At 11:00 p.m. EDT on Saturday the center of Hurricane Rachel was located at latitude 20.7°N and longitude 116.6°W which put it about 455 miles west-southwest of the southern tip of Baja California.  Rachel was moving toward the north-northwest at 7 m.p.h.  The maximum sustained wind speed increased to 85 m.p.h. and the minimum surface pressure decreased to 982 mb.

An upper level ridge over northern Mexico that was generating northeasterly winds over the top of Rachel weakened as a large upper level trough moved over the western U.S.  As the vertical wind shear decreased, a ring of thunderstorms developed around the core of the circulation.  The formation of an eye and a tight inner core allowed the wind speed to increase rapidly to hurricane intensity.  The core of Rachel will remain in an environment that could support further intensification during the next 12-18 hours.  Eventually, the upper level trough will increase the wind shear again and the hurricane will move over cooler Sea Surface Temperatures (SSTs).  Those factors will produce a weakening trend early next week.

The upper level trough is helping to pull Rachel northward.  However, it looks like the trough will move eastward before it can sweep Rachel toward the northeast.  Recent guidance from the numerical models suggest that as the trough moves away to the east, Rachel will stall.  If it stalls over cooler SSTs, then it will be steered more by lower level winds, once the tall thunderstorms around the eye dissipate.  Those winds could push the lower level remnant circulation slowly toward the west or southwest;

 

TD 18E Intensifies into Tropical Storm Rachel

Tropical Depression 18-E which formed earlier today has intensified into Tropical Storm Rachel.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Rachel was located at latitude 15.3°N and longitude 107.4°W which put it about 325 miles southwest of Manzanillo, Mexico and about 550 miles south-southeast of the southern tip of Baja California.  Rachel was moving toward the west at 12 m.p.h.  The maximum sustained wind speed was 40 m.p.h. and the minimum surface pressure was 1004 mb.

A strong upper level ridge over northern Mexico has been producing northeasterly winds and wind shear over the circulation of Rachel.  The wind shear has been the reason why most of the thunderstorms have been located west of the center of circulation.  The northeasterly winds diminished slightly during recent hours and more thunderstorms developed closer to the center.  The improved organization allowed the wind speed at the surface to increase and Rachel became a tropical storm.  The upper level winds could decrease further and some additional intensification is possible.

A ridge in the middle levels is likely to steer Rachel to the west-northwest during the next day or two.  As Rachel moves farther north, it could be affected by a mid-level trough (i.e. a shortwave trough) in the westerly flow in about 72 hours.  If Rachel is strong enough and tall enough, then the mid-level trough could turn Rachel back to the northeast, which could move it toward Baja California.  If Rachel is weaker and the circulation does not extend as high into the atmosphere, then the mid-level trough may not affect the movement of Rachel.  In that case, it would probably continue to move west and dissipate over cooler Sea Surface Temperatures.